I'm not familiar with the acronym CS:GO, so I Googled it. The top hit was for Counter-Strike: Global Offensive, which looks like a game. Was this a Windows game, or an Ubuntu game? If the former, you shouldn't have been able to install it on the same partition as Ubuntu (you say you installed both to
E:) unless you used the deprecated WUBI method of installing Ubuntu.
This raises a couple of important questions:
- Are you booting in BIOS mode, in EFI mode, or a mixture of the two? This is always a critical question when diagnosing boot problems. Your description of having "BIOS" (probably actually EFI) boot options of "Windows Boot Manager" and "Ubuntu" suggests EFI-mode, since BIOS-mode booting does not name OSes in this way -- at least, not in the firmware's built-in boot manager.
- Did you use WUBI? AFAIK, WUBI only works for BIOS-mode booting, and it's no longer recommended even for that. Your claim that you installed both Ubuntu and the game to
E: suggests use of WUBI; but perhaps you erred in your description or your Windows drive assignments changed at some point. Note that Ubuntu does not give drive letters like Windows, so if you installed Ubuntu in the normal way, describing it as being on
E: is meaningless; you'd do better to say what partition, as identified in Ubuntu, holds the OS, like
Answering these questions may help with a more specific analysis of your problem. The usual recommendation in your situation is to run Boot Repair. This tool can fix some common boot problems, including some that have the symptoms you describe; however, it might not work, and in rare cases it can actually make matters worse. Note that the question of your boot mode (BIOS vs. EFI) is very important, and it's critical that the emergency system you use to run Boot Repair run in the same mode as your regular OS installations. See this page of mine for information on determining your boot mode -- both in Windows and in the emergency disk you boot to run Boot Repair.
If you run Boot Repair and it doesn't help, please post the URL it provides; that will give us more information about your configuration. If you're not sure if you should use Boot Repair, you can go ahead and run it, but select the "Create BootInfo Summary" option. When asked whether to upload the report, click "Yes," and then post the URL provided here.